This invention relates to suspension systems for railcars and, more particularly, to suspension systems of this type which utilize elastomeric compression springs.
Most conventional suspension systems employ some sort of main spring element for supporting the sprung structure (e.g., the body of a vehicle in a vehicular suspension). In these suspension systems, conventional coil suspension springs are utilized most commonly as the main spring element; however, these springs deflect linearly in response to the application of compressive loads, or produce a linear load-deflection spring curve, and therefore are selected on the basis of the average anticipated suspension load. Above and below the average load, the spring provides insufficient and excessive spring force, respectively. In addition, conventional coil compression springs tend to bottom under high load or shock conditions. Typically, the compression limits of such springs are about one third their original length and, upon application of compressive loads or shock forces of sufficiently high magnitude, are compressed to the point that their coils bottom or come into metal to metal contact with one another. Coil springs, therefore, do not offer the most effective main sprin suspension means in many applications, especially railcar suspensions, subject to a wide range of load conditions, high magnitude shock forces or large displacements. Another disadvantage of coil springs is that they have little or no inherent damping, a property which is highly desirable in many vehicular suspension systems.
Elastomeric springs of the shear, or combination shear-compression type, have been used extensively in vehicular suspensions, particularly railcar suspensions; however, fears of environmental effects, cold flow, creep, fatigue and other failure phenomena have limited the usage of elastomeric springs to suspensions subject to small magnitude displacements or loads, or have required supplemental coil springs or load distribution devices to prevent over stressing of the elastomeric springs. Some known elastomeric compression springs, for example, employ end plates which are bonded to the opposed force bearing surfaces of the spring in order to increase the load bearing capacity of the spring. Destructive stress concentrations, however, tend to develop adjacent the end plate bonds under high compressive loads and may lead to bond breakage or rupture of the body of elastomeric material. Such bonded end plate elastomeric springs are disclosed in U.S. Pat. No. 3,461,816, issued to Beck and U.S. Pat. No. 2,154,586, issued to Stern. Elastomeric shear compression or sandwich springs, which typically employ flat inter-leaved rubber spring elements in V or chevron formations, suffer from similar problems.
Other types of known elastomeric compression springs employ solid bodies of elastomeric material of square or rectangular cross sectional configuration. In many practical applications, however, these springs tend to develop undersirable stress concentrations at the sharp corners between adjacent spring surfaces. Such stress concentrations may lead to rupture of the spring material under high compressive loads. Toroidal elastomeric springs of generally circular cross sectional configuration also have been proposed, as in U.S. Pat. No. 3,515,382, issued to Gallagher. Toroidal springs, however, are highly undersirable in many applications, especially vehicular suspension systems, in which the spring elements must be mounted and operated in a confined space. Furthermore, toroidal springs tend to develop destructive hoop stresses upon application of high compressive loads.
Another known type of elastomeric spring utilizes an elastic solid roller body, formed of natural or artificial rubber. The roller body rolls about its longitudinal axis between two spaced apart load application surfaces as they are moved relatively in rotational or translational fashion. The spring force obtained is produced as the roller body is rolled between the load application surfaces, in response to relative movement thereof, to a region of reduced spacing, where it is compressed radially. Such roller type elastomeric springs are disclosed in U.S. Pat. Nos. 2,712,742, 2,729,442, 2,819,063, 2,842,410, British Pat. No. 749,131 and German Pat. No. 2,189,897, all issued to Neidhart, and in U.S. Pat. No. 2,189,870, issued to Sluyter. The roller body or bodies employed in these roller type elastomeric springs, however, are subject to surface wear and destructive shear stresses which are produced by the rolling action between the load application surfaces. Additionally, destructive force couples, or torsional stresses, are produced as the force application axis, along which the compressive force of each load application surface is applied, shifts to one side or the other of the roller body centroid.
Still another known elastomeric spring which is generally similar to the roller type spring described previously except that the spring is compressed radially without rotational movement, is disclosed in U.S. Pat. No. 3,351,308, issued to Hirst. The arcuate load application surfaces between which the spring is squeezed or compressed radially surround and confine the spring, and hence prevent free bluging of diagonally opposed portions of the curved spring side surfaces under all load conditions, especially upon application of high compressive loads which tend to produce substantial flattening of the spring. Consequently, if restrained excessively from free deformation, the spring tends to rupture or fail. To limit total spring deflection, the top casting and base are formed so that they engage one another in response to application of a sufficiently high downward load or impact force. When engaged, however, forces are transmitted directly between the top casting and base, and hence the spring is ineffective. That is, the spring system comprising two load application surfaces and the elastic spring body, in effect, bottoms in much the same manner as a conventional coil spring. The end result is that this spring system is of limited usefulness, and is unsuitable for use in many practical spring applications, such as vehicular suspension systems, in which high load or impact forces are to be encountered. Further, in addition to being of arcuate configuration, the load application surfaces between which the spring is compressed initially are spaced apart diagonally. Consequently, the spring is squeezed therebetween or is deflected radially along a deflection axis which extends in a diagonally inclined direction between these surfaces in response to application of a downward load applied along a vertical load application axis. That is, the deflection axis (diagonal) does not coincide with the load application axis (vertical). The end result is that destructive torsional forces, force couples and shear stresses are produced in the elastic spring body. Futhermore, due to such non-symmetrical spring loading with respect to vertically applied loads, two parallel springs must be used. Another generally similar suspension for railcar useage is disclosed in U.S. Pat. No. 1,484,954, issued to Masury.
In addition to the main spring elements, another important factor in the design and selection of a suspension system is the damping or shock absorbing means. There is much concern in the mobile vehicle industry, particularly in the railcar and truck-trailer fields, regarding problems caused by dynamic forces which produce high frequency vibration, resonant motion, etc. Prior art damping systems which attempt to eliminate or minimize these problems have largely utilized hydraulic shock absorbers or constant force friction elements. Hydraulic damping is velocity responsive (rather than load responsive) and hence tends to produce damage to the lading for higher frequency forcing modes. Most prior friction dampers for railcar usage employ coil springs for actuating the friction shoe (see U.S. Pat. No. 3,517,620, issued to Weber) and thus produce a linear rate damping force. Examples of additional similar prior art dampers are disclosed in U.S. Pat. Nos. 3,338,183, 3,486,465 and 3,545,385. Consequently, such prior friction dampers suffer from many or all of the disadvantages of coil springs mentioned above and may even require supplemental damping by hydraulic shock absorbers.
One type of prior railcar suspension including a friction damper, which employs a rubber suspension pad for urging a friction shoe into frictional engagement with a friction surface, is disclosed in U.S. Pat. Nos. 2,356,743, and 2,357,264, both issued to Light, and in U.S. Pat. No. 2,295,554, issued to Cotrell. This suspension, however, due to the inclusion of coil springs as the main suspension spring elements, suffers from some or all of the above-mentioned disadvantages.